To make caramelised white chocolate ganache, preheat oven to 160°C. Scatter chocolate evenly over base of a shallow baking dish and bake for 20 minutes, stirring twice or until caramel in colour. Transfer to a large bowl. Bring cream almost to the boil in a small saucepan and whisk in chocolate until almost smooth. Strain mixture through a fine sieve, pushing down on solids; discard solids. Cover and refrigerate for 30 minutes, stirring occasionally, or until ganache is of a spreadable consistency.

Increase oven to 220°C.

Pour condensed milk into a 2-litre (8-cup) ceramic ovenproof dish. Cover dish with foil and crush excess foil upwards. Place ceramic dish in a larger baking dish and add enough boiling water to come halfway up side of the ceramic dish. Bake for 1 hour.

Stir mixture then cover and bake a further 30 minutes or until a golden caramel colour, adding extra boiling water to baking dish as needed to maintain water level during baking. Whisk caramel until smooth. Cover; cool to room temperature.

Reduce oven to 160°C. Grease a deep 20cm (8-inch) round cake pan; line base and side with baking paper.

In a medium saucepan, stir butter, sugar and salt over low heat, without boiling, until smooth. Add caramel and schnapps; whisk until smooth. Transfer mixture to a large bowl and cool for 15 minutes. Whisk in sifted flours, then eggs. Pour into pan.

Bake cake for 1 hour. Cover pan loosely with foil and bake another 1 hour or until a skewer inserted into the centre comes out clean. Stand cake in pan for 15 minutes before turning, top-side up, onto a wire rack to cool.

Place cake on a plate; spread top with ganache.